Method for manufacturing semiconductor element

ABSTRACT

A method for manufacturing a semiconductor element of the present invention, has: a laser irradiation step of focusing a pulsed laser beam inside of a substrate constituting a wafer, thereby forming a plurality of isolated processed portions along an intended dividing line inside of the substrate, and creating a fissure that runs from the processed portions at least to the surface of the substrate and links adjacent processed portions; and a wafer division step of dividing the wafer along the intended dividing line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This national phase application claims priority to Japanese PatentApplication No. 2009-041966 filed on Feb. 25, 2009. The entiredisclosure of Japanese Patent Application No. 2009-041966 is herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method for manufacturing asemiconductor element, and more particularly relates to a semiconductorelement manufacturing method comprising a step of dividing a wafer thatincludes a substrate.

BACKGROUND ART

The manufacture of a semiconductor element includes a step of dividing awafer into element chips, and a method in which separation grooves areformed with a cutter, dicer, or the like and the pieces snapped aparthas been used to divide these element chips. A method has been proposedin recent years in which a laser beam is used instead of a cutter ordicer to form separation grooves or the like, and the chips are thenbroken apart, but with a method in which a wafer is heated and melted bybeing irradiated with a laser beam, the places that are melted and thenre-solidify become discolored, and this decreases the brightness of alight emitting element, so a method has been proposed in which a pulsedlaser beam with a short pulse width is used to work the wafer. Using apulsed laser beam with a short pulse width allows working to beperformed that is free of discoloration because it involves multiphotonabsorption rather than melting, so there is less of a decrease in thebrightness of a light emitting element.

As shown in FIG. 12, a method that has been proposed for dividingelement chips using a pulsed laser beam with a short pulse width, inwhich a modification region 41 is formed by laser irradiation in aregion corresponding to an intended dividing line inside of a substrate40 provided with a semiconductor layer 42, and the chips are brokenalong this line (JP-2008-6492-A).

Also, as shown in FIG. 13, another method has been proposed in which aplurality of levels of modified components 51 are formed by laserirradiation inside of a substrate 50 provided with a semiconductor layer52, and a continuous groove 53 is formed by laser irradiation in thesurface of the substrate 50, so that the semiconductor light emittingelements are separated from a separation plane along the groove 53 andthe plurality of levels of modified components 51 (JP-2008-98465-A andJP-2007-324326-A).

SUMMARY

However, with a method in which a wafer is divided by forming amodification region with a pulsed laser beam only inside of a substrate,the application of external force creates a crack from the modificationregion inside toward the front and rear faces of the substrate, and thisis used to break the wafer, so it is difficult to control the directionin which the crack runs, and the wafer is sometimes divided somewhereother than in the intended division region.

Also, with a method in which grooves are formed by laser irradiation ina substrate surface, the means for forming the separation grooves, whichin the past were formed by cutter or dicer, is changed to a laser,making it difficult to control the direction in which the cracks run,just as when chips are split apart along separation grooves made with acutter or dicer. Furthermore, when a laser beam is focused on thesubstrate surface to form a groove, the laser beam may sometimes befocused on the outside of the substrate due to problems with thefocusing precision of the laser apparatus or to irregularity of thesubstrate surface. If the focal point is in the air outside thesubstrate, a plasma will be generated to a corresponding degree, andthis wastes some of the energy of the laser beam.

As a result of diligent research to solve the above problems, theinventors have discovered that the above problem can be solved bycreating processed portions, and a fissure that links adjacent processedportions and runs from the processed portions to the substrate surface.

A method for manufacturing a semiconductor element of the presentinvention has: a laser irradiation step of focusing a pulsed laser beaminside of a substrate constituting a wafer, thereby forming a pluralityof isolated processed portions along an intended dividing line inside ofthe substrate, and creating a fissure that runs from the processedportions at least to the surface of the substrate and links adjacentprocessed portions; and a wafer division step of dividing the waferalong the intended dividing line.

The following requirements can be combined to the method formanufacturing a semiconductor element of the present invention.

The fissure links adjacent processed portions inside of the substrate.

The processed portions have a top part and a bottom part, and thefissure links the top parts and bottom parts of adjacent processedportions.

The distance between the focal position of a pulsed laser beam and thesurface of the substrate is at least half a working spot diameter of thepulsed laser beam, and no more than 25 μm.

The distance between the focal position of the pulsed laser beam and thesurface of the substrate is at least 5 μm and no more than 25 μm.

The distance between processed portions is at least the working spotdiameter of the pulsed laser beam.

The processed portions and the fissures are formed within a range of atleast 10% and no more than 80% of the thickness of the substrate.

The intended dividing line is a first intended dividing line, and thefissure is a first fissure, the laser irradiation step further involvesfocusing the pulsed laser beam inside of the substrate along a secondintended dividing line that is substantially perpendicular to the firstintended dividing line, thereby forming a plurality of isolatedprocessed portions along an intended dividing line inside of thesubstrate, and creating a second fissure that runs from the processedportions at least to the surface of the substrate and links adjacentprocessed portions, and the wafer division step further involvesdividing the wafer along the second intended dividing line.

The first fissure goes roundaboutly adjacent processed portions, and thesecond fissure runs along the second intended dividing line.

The spacing of the processed portions formed along the first intendeddividing line is less than the spacing of the processed portions formedalong the second intended dividing line.

The substrate has a first main face and a second main face, asemiconductor layer is provided on the first main face, and the pulsedlaser beam is emitted from the second main face side in the laserirradiation step.

The distance between the focal position of the pulsed laser beam and thesemiconductor layer is greater than 30 μm.

The processed portions are produced by multiphoton absorption.

The substrate is a sapphire substrate.

The second main face is a plane different from the A plane, and thefirst intended dividing line is a line that intersects the axis of thesubstrate.

With laser irradiation, processed portions and a fissure that linksadjacent processed portions and runs from the processed portions to thesubstrate surface are created, which makes possible accurate splittingalong the processed portions or fissures. When the laser is directedalong the intended dividing line, first the fissure extends along theintended dividing line from the processed portions to the substratesurface, and furthermore, cracks extending from the processed portionsor the fissure can run along the intended dividing line to the back sideof the substrate. This allows the wafer to be divided accurately.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is simplified plan view illustrating the main steps in thisembodiment.

FIG. 2 is simplified plan view illustrating the main steps in thisembodiment.

FIG. 3 is a sectional view along A-A in FIG. 2.

FIG. 4 is a sectional view along B-B in FIG. 2.

FIG. 5 is a sectional view describing a step of an embodiment.

FIG. 6 is simplified sectional view illustrating the main steps in thisembodiment.

FIG. 7 is a schematic diagram describing part of the side face of thelight emitting device of an embodiment.

FIG. 8 is simplified plan view illustrating a step in this embodiment.

FIG. 9 is simplified plan view illustrating a step in this embodiment.

FIG. 10 is simplified plan view illustrating a step in this embodiment.

FIG. 11 is simplified sectional view illustrating a step in thisembodiment.

FIG. 12 is a diagrammatic perspective view describing a conventionalmanufacturing method.

FIG. 13 is a diagrammatic perspective view describing a conventionalmanufacturing method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method for manufacturing a semiconductor element in this embodimentcomprises a laser irradiation step of directing a laser along anintended dividing line, and a wafer division step of dividing the waferalong the intended dividing line. In the laser irradiation step, aplurality of processed portions are formed inside of the substrate byirradiation with a pulsed laser beam, and a fissure is generated thatruns from the processed portions at least to the surface of thesubstrate and links adjacent processed portions.

An embodiment of the method of the present invention will now bedescribed in detail through reference to the drawings. The drawings areschematic representations, and some parts may be exaggerated beyond whatthey actually are. Also, the present invention is not limited to or bythe following embodiments or Examples, and various modifications arepossible without departing from the technological concept of the presentinvention.

Laser Irradiation Step

FIGS. 1 and 2 are simplified plan views illustrating part of the mainsteps entailed by the method for manufacturing a semiconductor elementin this embodiment.

First, a wafer 1 that has a substrate 10 and is later divided intosemiconductor elements is irradiated with a laser along the intendeddividing line 11 shown in FIG. 1. As shown in FIG. 2, a plurality ofprocessed portions 12 that are separated from one another can be formedby focusing a pulsed laser beam inside of the substrate 10. At the sametime, a fissure 13 can be created that runs from the processed portions12 at least to the surface of the substrate 10 and that links adjacentprocessed portions 12. Although not depicted in the drawings, a fissureis sometimes produced on the substrate surface that extends in adifferent direction from that of the fissure linking the processedportions. The wafer can be divided accurately by creating a fissure thatlinks at least adjacent processed portions. It is preferable here if thefissure runs from all of the processed portions 12 to the surface of thesubstrate 10, but the fissure runs from at least a plurality ofprocessed portions to the surface of the substrate. It is preferable tocreate a fissure that will link all of the adjacent processed portions,but the fissure at least links adjacent processed portions at aplurality of locations. Furthermore, it is preferable to create afissure that runs to the surface of the substrate and a fissure thatreaches to adjacent processed portions for a single processed portion,but a fissure that runs to the surface of the substrate and a fissurethat links adjacent processed portions may be formed at differentprocessed portions.

FIG. 2 shows the locations of the processed portions 12 for the sake ofdescription, but the actual processed portions 12 are formed inside ofthe substrate 10 as shown in FIG. 3. FIG. 3 is a simplified crosssection as viewed from the A-A line in FIG. 2. A semiconductor layer 14is provided on a first main face 10 a of the substrate 10. The processedportions 12 are formed inside of the substrate 10 by laser irradiation,and the fissure 13 is created from the processed portions 12 to a secondmain face 10 b of the substrate. Such linking adjacent processedportions 12 with the fissure 13 results in a linear fissure 13 that runslong an intended dividing line being produced on the surface of thesubstrate 10, as shown in FIG. 2. The fissure is created from theprocessed portions. That is, the processed portions are formed near thefocal positions by focusing a pulsed laser beam inside of the wafer, andit is believed that compression stress occurs around these locations,and that the fissure is created by this compression stress.

When the processed portions are thus formed, as will be discussed below,the processed portions and the fissure can be suitably formed bystrictly controlling one or more of, and preferably all of, thefollowing: the means for forming the processed portions (such as using apulsed laser), the laser energy, frequency, or pulse width, the spotdiameter or shape of the processed portions, and the positions of theprocessed portions inside of the substrate (such as the depth of theprocessed portions from the substrate or semiconductor layer, or thespacing between the processed portions).

The pulsed laser beam can be selected from those capable of processinginside of a substrate, and more specifically, the amount of energy perpulse is favorably 0.8 to 5 μJ, and preferably 0.8 to 2.5 μJ. Thefrequency is favorably 50 to 200 kHz, and preferably 50 to 100 kHz. Thepulse width is favorably selected from a range over which working bymultiphoton absorption is possible, in order to form processed portionswith which there will be no optical absorption due to discoloration. Anexample is a range of 300 to 50,000 fs. Setting the pulse width towithin this range prevents discoloration caused by resolidificationafter the melting of the processed portions. This is particularlyeffective when the semiconductor elements obtained after dividing arelight emitting elements.

The focal position of the laser beam is favorably selected from a regionin which the processed portions do not reach the substrate surface, andthe depth from the substrate surface is preferably at least half theworking spot diameter. A depth of 5 μm or more is preferable when takinginto account error of the laser apparatus or irregularity of thesubstrate surface. In the case of a wafer having a semiconductor layeron the opposite side from the substrate surface (hereinafter sometimesreferred to as the “back side”), typically there is a risk of damage tothe semiconductor layer if the distance between the focal position andthe semiconductor layer is 30 μm or less, so the distance from thesemiconductor layer is preferably greater than 30 μm. The distance fromthe substrate surface in this case is favorably 50 μm or less, with 25μm or less being preferable, and 10 μm or less even better.

The distance between the processed portions on the substrate surfaceproduced by the laser beam directed along the intended dividing linetypically is substantially constant, and is selected from a range thatwill produce a fissure at least linking the processed portions on thesubstrate surface. More specifically, the distance between the processedportions is preferably one to four times the working spot diameter. Itis preferable here if the fissure is produced between all of theprocessed portions 12, but the fissure should be produced between atleast a plurality of the processed portions. If the distance between theprocessed portions is too short, it is believed that compression stresswill be produced by the next laser irradiation in the region wherecompression stress was produced by the previous laser irradiation, thestresses in this region will cancel each other out, and the processedportions will not be linked by a fissure. Accordingly, to link theprocessed portions with a fissure inside of the substrate as well, thedistance between the processed portions is favorably set to be at leastthe working spot diameter on a plane parallel to the substrate mainface, and is preferably one to four times the working spot diameter, andmore preferably 1.5 to 3 times. It is believed that if the compressionstress reaches deep into inside of the substrate, the division will tendto be along the intended dividing line substantially perpendicular tothe substrate surface, so it is preferable to create compression stressbetween processed portions inside of the substrate as well, as discussedabove. Also, a wafer can be accurately divided in just a single stage ofworking, as shown in FIG. 3, by thus having this compression stress godeep into the substrate.

The spot diameter (φμm) of the laser beam can be calculated from thefollowing equation. λ is the wavelength (μm) of the laser beam, D is thelaser beam emitted spot diameter (φμm), and f is the focal distance (μm)of an objective lens. Preferably, the positions of the processedportions are adjusted by factoring in the effect of deviation from thetheoretical spot diameter due to the actual working situation. Morespecifically, the diameter of the processed portions formed in thesubstrate is preferably adjusted as the working spot diameter.Spot diameter (φμm)=(4·λ·f)/π·D

The pulsed laser beam is preferably emitted from the substrate main faceside on which the fissure linking the processed portions is to run. Thisis because stress tends to accumulate on the laser beam irradiationside, and it is easier to generate a fissure that extends from theprocessed portions to the substrate surface. Typically, the laser isemitted from the substrate main face side closer to the focal positionof the laser beam, that is, closer to the positions where the processedportions will be formed. For example, when the fissure is made to run tothe second main face 10 b as with the wafer 1 shown in FIG. 3,preferably the laser beam is emitted from the second main face 10 b, sothat the processed portions 12 are formed toward the second main face 10b.

FIG. 4 is a simplified cross section as viewed from the B-B line in FIG.2. The processed portions 12 have a shape that is longer in thedirection of laser irradiation, and when the laser irradiation isperformed from directly over the substrate, the shape is longer in thedepth direction of the substrate, as shown in FIG. 4. The fissure iscreated in the range of the hatching going upward to the right in FIG.4, for example. The fissure generated in this hatched area extends fromthe processed portions 12 to the second main face 10 b, and at leastlinks the processed portions 12 on the substrate surface. Usually, theprocessed portions extend to the substrate surface side from the focalposition of the laser beam, so the distance from the processed portionsto the substrate surface is less than the distance from the focalposition of the laser beam to the substrate surface.

The fissure is generated around the processed portions, and preferablylinks adjacent processed portions inside of the substrate as well. It issurmised that thus forming the fissure down deep results in thecompression stress produced by laser irradiation being generated downdeep. Consequently, it is believed that the substrate tends to bedivided along the laser irradiation direction. If the processed portionsare linked by a fissure inside of the substrate, it is believed that thefissure can be made to run from the processed portions to the substratesurface by setting the distance from the processed portions to thesubstrate surface to be no more than the distance between the processedportions, and preferably to no more than half the distance between theprocessed portions.

The depth of the fissure can be adjusted by controlling the compressionstress imparted by laser irradiation. For example, as shown in FIG. 5,the fissure can be formed more shallowly than in FIG. 4. This depth ofthe fissure can be adjusted by controlling one or more of theirradiating laser wavelength, frequency pulse waveform, pulse width,focal precision, working feed rate, and position or shape of theprocessed portions. In addition, examples of methods for impartingcompression stress to the substrate include one in which the substrateis ground and polished prior to laser irradiation, and one in which theface of the substrate on the laser irradiation side is held so that itwill become concave during laser irradiation. It is believed that thefissure can be formed more deeply by expanding the compression stresswidth range.

Wafer Division Step

As shown in FIG. 6, a crack 15 is made to run from the processedportions 12 or the fissure 13 to the first main face 10 a side, and thewafer is divided along an intended dividing line. This division can beaccomplished by a known method, such as pressing a breaking knifeagainst the wafer along the intended dividing line and then applyingenough force to split the wafer.

FIG. 6 is a simplified cross section as viewed from the same directionas in FIG. 3, and illustrates part of the main steps in the method formanufacturing a semiconductor element of this embodiment. The fissure 13links adjacent processed portions 12 as discussed above, that is, thefissure 13 links them linearly along the intended dividing line on thesecond main face 10 b of the substrate 10. Consequently, the crack 15can be made to run along the intended dividing line in the same manneras the fissure 13, and the wafer 1 can be divided accurately along theintended dividing line. Here, the wafer is preferably divided along atleast part of the fissure, and it is not necessary for the face obtainedby division to conform perfectly to the fissure. Some of the fissure mayremain inside of or on the surface of the substrate after division.

Some trace of the processed portions and fissure can usually bediscerned on the side faces of the semiconductor elements obtained bydividing the wafer. More specifically, as shown in FIGS. 4 and 5discussed above, the processed portions 12, which do not extend to thesubstrate surface, typically are spaced apart at substantially constantintervals, and irregularity produced by the fissure remains from theprocessed portions 12 all the way to the substrate surface. Thisirregularity can be seen as the hatching that goes upward to the rightin FIGS. 4 and 5. The processed portions and irregularity is seen over arange of about 5 to 30 μm from the substrate surface, for example, onthe side faces obtained by division.

FIG. 7 is a schematic diagram of the part of the face obtained bydivision that is close to the second main face 10 b. The processedportions 12 provided away from the second main face 10 b of thesubstrate 10 have top parts 12 a and bottom parts 12 b, and the face offine irregularity 16, which is surmised to be produced by the fissure,links the top parts 12 a and bottom parts 12 b of adjacent processedportions 12. The processed portions 12 are apart from the second mainface 10 b of the substrate 10, and the distance between the second mainface 10 b and the processed portions 12 can be set to about 1 μm ormore. More specifically, this distance is about 1 to 15 μm. The lengthof the processed portions 12 can be set to about 5 to 30 μm. The lengthof the top parts 12 a can be set to about 3 to 10 μm. The irregularity16 decreases moving away from the second main face, and tends to bealmost invisible far away from the bottom parts. The height differenceof the irregularity 16 is a few microns or less, such as 2 μm or less.When the side face is observed after division, the bottom parts of theprocessed portions are hard to tell apart from irregularity caused bythe fissure, but the irregularity region extending continuously from thetop part to the first main face side in substantially linear fashion canbe considered to be the bottom part. Also, when processed portions areformed by the multiphoton absorption of a laser beam, the top parts ofthe processed portions can be recognized as particularly smooth faces.

As shown in FIG. 7, when the processed portions have top parts andbottom parts, the fissure preferably links at least adjacent top parts,and more preferably also links adjacent bottom parts. The closer to thedistal end side of the bottom part on the opposite side from the toppart, the more difficult linking by the fissure tends to be. A processedportion component in which the top part is present on the second mainface side can be formed by irradiating with a laser beam from the secondmain face side, for example. The size of the processed portions and theirregularity can be varied according to the thickness of the substrate,and the numerical ranges given above are particularly favorable whendividing a substrate with a thickness of about 50 to 150 μm. The rangeover which the processed portions and irregularity are formed isfavorably at least approximately 10% of the thickness of the substrate,with approximately 80% or less being preferable, and approximately 40%or less being even better. The use of this range allows the substrate tobe divided efficiently and prevents damage to the semiconductor layer.

Wafer

The term “wafer” usually means a flat base that is grown in from a rawmaterial substance in a columnar shape called an ingot, and then slicedthinly. In this application, just this flat base may be the “substrate”referred to below, or it may be made into a wafer in a state in which asemiconductor layer, a dielectric layer, an insulator layer, a conductorlayer, or the like are laminated in one or more layers on thissubstrate.

Substrate 10

The material of the substrate can be selected from among those that canbe processed with a pulsed laser beam. More specifically, sapphire,silicon, SiC, GaAs, GaN, AlN, and the like can be used. Typically, amaterial on which a semiconductor layer can be grown is selected for thesubstrate. With a sapphire substrate, the division plane tends not to bealong the crystal orientation, and when an external force is exerted tosplit the substrate, it may be divided in a different direction from theintended dividing line, so division accuracy can be improved by usingthe method of this embodiment. There are no particular restrictions onthe thickness of the substrate, but it may be 50 to 150 μm, for example.Forming processed portions by the method of this embodiment in asubstrate with a thickness such as this allows the wafer to be dividedwithout the need for performing laser working a plurality of levels ofmodification.

As shown in FIG. 8, depending on the material of the substrate and thedirection of the intended dividing line, the fissure 13 that links theprocessed portions 12 may undulate. That is, the fissure 13 may goroundaboutly the adjacent processed portions 12. The angle of thefissure to a straight line connecting adjacent processed portions tendsto be a function of the crystal system of the substrate material, ormore specifically, can be selected from a range of about 10 to 70degrees. With an intended dividing line or substrate material with whichsuch a fissure is readily produced, it is believed that reducing thedistance between the processed portions makes the fissure closer to astraight line connecting the shortest distance between processedportions, but from the standpoint of energy efficiency, it is preferableto use a fissure 13 that go around as shown in FIG. 8. Since thisfissure links the processed portions, even if it should deviate from astraight line connecting the processed portions, the distance of thisdeviation is only about 0.5 to 10 μm at most, and creating a fissuresuch as this allows the wafer to be divided at a plane substantiallyperpendicular to the substrate main face. For example, with a sapphiresubstrate having a hexagonal system, the substrate surface through whichthe fissure runs is a plane other than the A plane, and when theintended dividing line is a line that intersects the a axis of thesubstrate, the resulting fissure tends to detour between the processedportions. This tendency is particularly pronounced when using a sapphiresubstrate whose main plane is the C plane. The “sapphire substrate whosemain plane is the C plane” mentioned here may be one in which the mainplane is a plane that is inclined by a few degrees from the C plane.

A light emitting element is usually substantially square orsubstantially rectangular, and two kinds of line that intersectsubstantially at a right angle are set as the intended dividing lines.In the case of a sapphire substrate or other such substrate with ahexagonal system, if one intended dividing line is set in a direction ofrelatively easy division, another intended dividing line that issubstantially perpendicular to it is set in a direction of difficultdivision.

For example, as shown in FIG. 9, if first processed portions 22 a alonga first intended dividing line and second processed portions 22 b alonga second intended dividing line are formed inside of a wafer 2, a secondfissure 23 b that links the second processed portions 22 b runssubstantially linearly along the second division line, whereas a firstfissure 23 a that links the first processed portions 22 a runsroundaboutly the first processed portions 22 a. When a sapphiresubstrate whose main plane is the C plane is used as the substrate, ifthe first intended dividing line is a line substantially parallel to them axis of the substrate, and the second intended dividing line is a linesubstantially parallel to the a axis of the substrate, the secondfissure will tend to run in a substantially linear shape, which ispreferable.

If the first fissure undulates and the second fissure runs substantiallylinearly, it is believed that the direction of the second intendeddividing line affords easier division than the direction of the firstintended dividing line, so as shown in FIG. 10, the wafer can beefficiently divided by having the distance between the second processedportions 22 b greater than the distance between the first processedportions 22 a inside of the substrate 20.

The method of this embodiment can be used only in the division of thefirst intended dividing line, and a division at the second intendeddividing line can be made with a cutter scribe, for example.

Furthermore, with the method of this embodiment, it does not matterwhether the first fissure or the second fissure, that is, the firstintended dividing line or the second intended dividing line, is formedfirst.

Semiconductor Layer 14

A semiconductor layer composed of any of various semiconductor materialscan be selected as the semiconductor layer, an example of which is agallium nitride compound semiconductor layer. More specifically, anexample is a compound expressed by In_(x)Al_(y)Ga_(1-x-y)N (0≦x≦1,0≦y≦1, 0≦x+y≦1). The semiconductor layer is usually produced bylaminating a first conductive layer, a light emitting layer, and asecond conductive layer in that order (starting from the substrate side)over a sapphire substrate, and may contain one or more n-type impuritiessuch as silicon, germanium, tin, sulfur, oxygen, titanium, zirconium,cadmium, or other such group IV elements, group VI elements, or thelike, or may contain a p-type impurity such as magnesium, zinc,beryllium, manganese, calcium, or strontium, as a first or secondconductivity type of impurity.

There are no particular restrictions on the method for growing thesemiconductor layer, and any method known as a semiconductor growthmethod can be used favorably, such as MOVPE (metal organic vapor phaseepitaxy), MOCVD (metal organic chemical vapor deposition), HVPE (hydridevapor phase epitaxy), or MBE (molecular beam epitaxy). MOCVD isparticularly favorable because it grows the material with goodcrystallinity.

Since the semiconductor layer is usually thinner than the substrate, if,as shown in the above-mentioned FIG. 6, the semiconductor layer 14 isformed on the first main face 10 a of the substrate 10, and theprocessed portions 12 are formed on the second main face 10 b side, thenthere is no need to remove the semiconductor layer 14 directly under theprocessed portions 12, and the semiconductor layer 14 can be divided atthe same time by means of the crack 15 extending from the substrate 10.Irradiation with a laser beam from the second main face side ispreferable in order to minimize damage to the semiconductor layer.Division can be similarly performed when forming the processed portionson the first main face side on which the semiconductor layer isprovided.

As shown in FIG. 11, when processed portions 32 are formed inside of asubstrate 30 on the first main face 30 a side in a wafer 3 having thesubstrate 30 and a semiconductor layer 34 provided on the first mainface 30 a of the substrate 30, prior to laser irradiation asemiconductor layer 34 is removed along the intended dividing line fromthe region corresponding to the locations where the processed portions32 will be formed, after which the processed portions 32 are formed anda fissure 33 is made to run up to the first main face 30 a, whichprevents damage to the semiconductor layer by laser irradiation. In thiscase, the irradiation with the laser beam is preferably performed fromthe first main face side.

Example 1

A wafer was prepared in which a GaN-based semiconductor layer was formedon one main face of a sapphire substrate with a thickness ofapproximately 85 μm. The semiconductor layer was produced by laminatingan n-type semiconductor layer, a light emitting layer, and a p-typesemiconductor layer in that order, starting from the sapphire substrateside, on the (0001) plane of the sapphire substrate.

After this, part of the light emitting layer and p-type semiconductorlayer are removed to expose the n-type semiconductor layer, and an nelectrode is formed on the n-type semiconductor layer surface, and a pelectrode on the p-type semiconductor layer surface.

To obtain a substantially square element measuring approximately 250 μmon one side, the intended dividing lines of the wafer were set in twodirections, one substantially parallel and one substantiallyperpendicular to the a axis of the sapphire substrate, and a pulsedlaser beam was directed along each of the intended dividing lines fromthe other main face side of the sapphire substrate, using a nearinfrared laser with an output of approximately 0.2 W. The focal positionof the laser beam was set to a depth of approximately 5 μm from thesubstrate surface, and the distance from a previous focal position tothe next focal position was set to approximately 3.5 μm.

After laser irradiation, a light source was disposed on thesemiconductor layer side, and observation was made with an opticalmicroscope from the other main face side of the sapphire substrate,which confirmed substantially circular processed portions and a fissureextending from the processed portion, and also confirmed that at leastpart of the fissure ran so as to link the processed portions on thesubstrate surface. A comparison of the fissures linking the processedportions along the intended dividing lines in the two directions revealsthat the fissure along the intended dividing line substantiallyperpendicular to the a axis undulates more than the fissure along theintended dividing line substantially parallel to the a axis.

Next, a breaking blade was pressed against the wafer along the intendeddividing lines, force was exerted to split the wafer, and substantiallysquare semiconductor elements measuring approximately 250 μm on one sidewere obtained. The elements thus obtained were observed, which confirmedthat the side faces of the elements had been divided substantiallyperpendicular to the sapphire substrate surface, and that processedportions extending linearly in the depth direction of the substrate werenear the substrate surface. No discoloration of the processed portionswas seen, and it is surmised that they were formed by multiphotonabsorption produced by laser irradiation. The distance from theprocessed portions to the substrate surface was about 1 to 10 μm, themaximum width of the processed portions was about 0.5 to 2 μm, andirregular bumpiness was confirmed from the processed portions to thesubstrate surface.

It is surmised that the irregularity was formed by the fissures, and thesame irregularity was confirmed on the faces between processed portions.The processed portions and the irregularity surfaces were formed to adepth of about 15 to 20 μm from the substrate surface. Deeper surfaces,that is, those on the semiconductor layer side, were either flat orcomprised a series of stepped flat surfaces, and were surmised to besurfaces divided after laser irradiation.

Example 2

In this example, semiconductor elements are manufactured in the samemanner as in Example 1, except that the distance between the focalpositions of the laser beam is set to approximately 5 μm in irradiationwith the laser beam along an intended dividing line substantiallyparallel to the a axis.

After laser irradiation, the sapphire substrate surface is observed,which confirmed the presence of substantially circular processedportions and a fissure extending from the processed portions, andconfirmed that at least part of the fissure ran so as to link theprocessed portions on the substrate surface. After wafer division thesemiconductor elements thus obtained are observed, which revealed thatthe element side faces is divided substantially perpendicular to thesapphire substrate surface.

The manufacturing method of the illustrated embodiments can be appliedto elements that are made into elements by the division of a waferhaving a substrate. It can be applied to a semiconductor element inwhich a semiconductor layer is provided on a substrate, and can beapplied to a light emitting element such as an LED or LD, a lightemitting element that also includes a light receiving element, or asemiconductor element that includes a transistor, such as an HEMT orFET.

DESCRIPTION OF THE NUMERALS

1, 2, 3: wafer; 10, 20, 30: substrate; 10 a, 30 a: first main face; 10b, 30 b: second main face; 11: intended dividing line; 12, 32: processedportion; 12 a: top part; 12 b: bottom part; 13, 33: fissure; 14, 34:semiconductor layer; 15: crack; 16: irregularity; 22 a: first processedportion; 22 b: second processed portion; 23 a: first fissure; 23 b:second fissure; 40, 50: substrate; 41: modification region; 51: modifiedcomponent; 53: groove; and 42, 52: semiconductor layer.

The invention claimed is:
 1. A method for manufacturing a semiconductorelement, comprising: a laser irradiation step of focusing a pulsed laserbeam inside of a sapphire substrate constituting a wafer, therebyforming a plurality of isolated processed portions inside of thesubstrate along an intended dividing line extending in a directionparallel to a main face of the substrate, and creating a fissure thatruns from the processed portions at least to the main face of thesubstrate and links adjacent processed portions aligned along thedirection parallel to the main face of the substrate; and a waferdivision step of dividing the wafer along the intended dividing lineafter the laser irradiation step.
 2. The method for manufacturing asemiconductor element according to claim 1, wherein the fissure linksadjacent processed portions inside of the substrate.
 3. The method formanufacturing a semiconductor element according to claim 2, wherein theprocessed portions have a top part and a bottom part, and the fissurelinks the top parts and bottom parts of adjacent processed portions. 4.The method for manufacturing a semiconductor element according to claim1, wherein the distance between the focal position of the pulsed laserbeam and the main face of the substrate is at least half a working spotdiameter of the pulsed laser beam, and no more than 25 μm.
 5. The methodfor manufacturing a semiconductor element according to claim 1, whereinthe distance between the focal position of the pulsed laser beam and themain face of the substrate is at least 5 μm and no more than 25 μm. 6.The method for manufacturing a semiconductor element according to claim1, wherein the distance between processed portions is at least theworking spot diameter of the pulsed laser beam.
 7. The method formanufacturing a semiconductor element according to claim 1, wherein theprocessed portions and the fissures are formed within a range of atleast 10% and no more than 80% of the thickness of the substrate.
 8. Themethod for manufacturing a semiconductor element according to claim 1,wherein the intended dividing line is a first intended dividing line,and the fissure is a first fissure, the laser irradiation step furtherinvolves focusing the pulsed laser beam inside of the substrate along asecond intended dividing line that is substantially perpendicular to thefirst intended dividing line, thereby forming a plurality of isolatedprocessed portions along an intended dividing line inside of thesubstrate, and creating a second fissure that runs from the processedportions at least to the main face of the substrate and links adjacentprocessed portions, and the wafer division step further involvesdividing the wafer along the second intended dividing line.
 9. Themethod for manufacturing a semiconductor element according to claim 8,wherein the first fissure goes roundaboutly adjacent processed portions,and the second fissure runs along the second intended dividing line. 10.The method for manufacturing a semiconductor element according to claim8, wherein the spacing of the processed portions formed along the firstintended dividing line is less than the spacing of the processedportions formed along the second intended dividing line.
 11. The methodfor manufacturing a semiconductor element according to claim 1, whereinthe substrate has a first main face and a second main face, asemiconductor layer is provided on the first main face, and the pulsedlaser beam is emitted from the second main face side in the laserirradiation step.
 12. The method for manufacturing a semiconductorelement according to claim 11, wherein the second main face is a planedifferent from the A plane, and the intended dividing line is a linethat intersects the a axis of the substrate.
 13. The method formanufacturing a semiconductor element according to claim 11, wherein thedistance between the focal position of the pulsed laser beam and thesemiconductor layer is greater than 30 μm.
 14. The method formanufacturing a semiconductor element according to claim 1, wherein theprocessed portions are produced by multiphoton absorption.
 15. Themethod for manufacturing a semiconductor element according to claim 1,wherein the fissure at least links the processed portions on the mainface of the substrate.
 16. The method for manufacturing a semiconductorelement according to claim 1, wherein the substrate has a first mainface and a second main face, the fissure that runs at least to the mainface of the substrate is formed on the first main face of the substrate,and the division of the wafer is performed by a crack that runs from atleast one of the processed portions and the fissure to the second mainface in the wafer division step.
 17. The method for manufacturing asemiconductor element according to claim 1, wherein the pulse width ofthe pulsed laser beam is in a range of 300 to 50,000 fs.